Optical film assembly and display device

ABSTRACT

Microstructured optical films, assemblies of films including at least one microstructured optical film, and (e.g. illuminated) display devices including a single microstructured optical film or assembly.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/422,900,filed Jun. 8, 2006, now U.S. Pat. No. 7,622,164 which is acontinuation-in-part of U.S. patent application Ser. No. 10/870,366filed Jun. 17, 2004 now abandoned; a continuation-in-part of U.S. patentapplication Ser. No. 10/939,184, filed Sep. 10, 2004, issued as U.S.Pat. No. 7,179,513; a continuation-in-part of U.S. patent applicationSer. No. 10/938,006, filed Sep. 10, 2004, issued as U.S. Pat. No.7,289,202; a continuation-in-part of U.S. patent application Ser. No.11/078,145 filed Mar. 11, 2005, issued as U.S. Pat. No. 7,282,272; andclaims priority to PCT application No. US2005/021351, filed Jun. 16,2005, published as WO2006/028543.

BACKGROUND

Certain microreplicated optical products, such as described in U.S. Pat.Nos. 5,175,030 and 5,183,597, are commonly referred to as “brightnessenhancing films”. Brightness enhancing films are utilized in manyelectronic products to increase the brightness of a backlit flat paneldisplay such as a liquid crystal display (LCD) including those used inelectroluminescent panels, laptop computer displays, word processors,desktop monitors, televisions, video cameras, as well as automotive andaviation displays.

Brightness enhancing films desirably exhibit specific optical andphysical properties including the index of refraction of a brightnessenhancing film that is related to the brightness gain (i.e. “gain”)produced. Improved brightness can allow the electronic product tooperate more efficiently by using less power to light the display,thereby reducing the power consumption, placing a lower heat load on itscomponents, and extending the lifetime of the product.

Brightness enhancing films have been prepared from high index ofrefraction monomers that are cured or polymerized, as described forexample in U.S. Pat. Nos. 5,908,874; 5,932,626; 6,107,364; 6,280,063;6,355,754; as well as EP 1 014113 and WO 03/076528.

Although various brightness enhancing films are known, industry wouldfind advantage in optical films such as brightness enhancing films andassemblies including at least one optical film having improvedproperties, such as higher gain. Such films and assemblies can beutilized in a display device.

SUMMARY

Presently described are optical films (e.g. suitable for directinglight) comprised of a light transmissible polymeric material having amicrostructured surface such as a repeating pattern of linear prisms.

In one embodiment, the film is a substantially non-polarizing filmhaving a single sheet relative gain of at least 1.78.

In another embodiment, the film is a reflective polarizing film having asingle sheet relative gain of at least 2.46. The microstructured surfacemay comprise a pattern of substantially parallel prisms orthogonal tothe pass axis of a reflective polarizing base layer film.

In other embodiments, the invention relates to assemblies comprising afirst microstructured optical film proximate a second optical film.

In other embodiments, the invention relates to display devise comprisingan embodied optical film or an embodied assembly proximate alight-emitting surface.

In one aspect, the assembly comprises a first microstructured opticalfilm proximate a non-structured reflective polarizing film and gain ofthe assembly of the first film and polarizing film is at least 2.59. Insuch an assembly, prisms of the microstructured optical film arepreferably orthogonal to the pass axis of the reflective polarizingfilm.

In another aspect, the assembly comprises a first substantiallynon-polarizing microstructured optical film proximate a secondsubstantially non-polarizing microstructured optical film wherein therelative gain of the assembly of the first and second films is at least2.80. The second film is positioned such that the prisms are nonparallel(e.g. 90°+/−20°) to the prisms of the first film. This assembly mayfurther include a third optical film (such as a non-structuredreflective polarizer) between or proximate the assembly first or secondoptical film. This assembly of three films may have a relative gain ofat least 3.40.

In another aspect, the assembly comprises a microstructured reflectivepolarizing film proximate a microstructured substantially non-polarizingoptical film and the relative gain of the assembly of first and secondfilm is at least 3.33.

In yet another aspect, an assembly of optical films is describedcomprising a first optical film having a microstructured surfacecomprised of a light transmissible polymeric material comprising atleast 10 wt-% inorganic nanoparticles proximate a second optical film.

In each of these embodiments, the microstructured surface preferablycomprises the reaction product of a polymerizable resin having arefractive index of at least 1.61. Further, the polymerizable resinpreferably has a low absorbance. The microstructured surface typicallycomprises the reaction product of a polymerizable composition comprisingat least one ethylenically unsaturated monomer, optionally at least oneethylenically unsaturated oligomer, and at least 10 wt-% inorganicnanoparticles. Zirconia is a preferred inorganic nanoparticle. Theinorganic nanoparticles are preferably fully condensed surface modifiedinorganic nanoparticles.

The optical film may comprise a base layer coupled to themicrostructured surface. For embodiments wherein the base layer has ahigh-index axis and the microstructured surface comprises parallelprisms, the prisms are preferably aligned 90 degrees +/−20 degrees tothe high-index axis of the base layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an illustrative microstructure-bearingoptical product of the present invention.

FIG. 2 is a schematic view of an illustrative backlit liquid crystaldisplay including the brightness enhancing film of the invention.

FIG. 3 is an exemplary plot of absorbance as a function of wavelength oftwo different polymerizable compositions.

FIG. 4 is an exemplary conoscopic plot of luminance emitted from aliquid crystal display.

DETAILED DESCRIPTION

The present invention relates to microstructured optical films,assemblies of films including at least one microstructured optical film,and (e.g. illuminated) display devices including a singlemicrostructured optical film or assembly.

In general, optical films are light transmissible films. Many opticalfilms are designed to modify the wave vectors and resultant ray paths oflight passing through the film. This may be accomplished for example byincorporation of a microstructured surface, a matte surface, a specularsurface as well as bulk diffusive properties.

As used herein, the term “film” refers to a generally planar structuretypically having a thickness substantially smaller (e.g. at least 10times) than its width and length. The thickness of an optical film istypically at least 25 microns. Although the thickness can be as great as3 cm for example, typically the film is less than 2 mm, and moretypically less than 800 microns.

A preferred type of optical film includes a microstructured surface suchas a plurality of prisms on the film surface such that the films can beused to redirect light through reflection and refraction (e.g. of adiffuse light source). Such films are known as brightness enhancingfilms and light management films.

A typical brightness enhancing film includes a microstructured surfacehaving a regular repeating pattern of symmetrical tips and grooves.Other examples of groove patterns include patterns in which the tips andgrooves are not symmetrical and in which the size, orientation, ordistance between the tips and grooves is not uniform.

Referring to FIG. 1, a microstructured optical film 30 may comprise abase layer 2 and a microstructured optical layer 4. Alternatively, themicrostructured optical film may be monolithic wherein the base layerand optical layer are comprised of the same material. Monolithicmicrostructured optical films can be prepared by known methods such asby extrusion of a molten thermoplastic resin. Optical layer 4 comprisesa linear array of regular right prisms, identified as prisms 6, 8, 12,and 14. The height of the prisms typically ranges from about 1 to about75 microns. Each prism, for example, prism 6, has a first facet 10 and asecond facet 11. The prisms 6, 8, 12, and 14 are formed on base 2 thathas a first surface 18 on which the prisms are formed and a secondsurface 20 that is substantially flat or planar and opposite firstsurface 18. By right prisms it is meant that the apex angle α istypically about 90°. However, this angle can range from 70° to 120° andmay range from 80° to 100°. Further the apexes can be sharp, rounded,flattened or truncated. The apex angle of rounded prisms can beapproximated by the intersection of the (e.g. flat) facets. The prismfacets need not be identical, and the prisms may be tilted with respectto each other. The prism heights of the array may be substantially thesame or may vary. The relationship between the total thickness 24 of theoptical article, and the height 22 of the prisms, may vary. However, itis typically desirable to use relatively thinner optical layers withwell-defined prism facets. A typical ratio of prism height 22 to totalthickness 24 is generally between 25/125 and 2/125.

Provided that the optical film functions to redirect light, the surfacestructures may have varying pitch, intersecting channels, and/or varyingprism angles. For example, the surface structures may have apseudo-random prism undulation, such as described in U.S. Pat. No.6,322,236. The surface structures may have more than three facets, andthus have other shapes such as pyramids. Further, the facets may berounded facets and/or have other non-triangular shapes. Depending on theshape, the surface structures may be non-prismatic.

Many polymeric materials can be used as a base material and/ormicrostructured optical layer. Suitable materials are sufficientlyoptically clear and structurally strong to be assembled into or usedwithin a particular optical product. Preferably, the base material ischosen that has sufficient resistance to temperature and aging thatperformance of the optical product is not compromised over time.

The particular chemical composition and thickness of the base materialand/or microstructured optical layer can depend on the requirements ofthe particular optical product that is being constructed. That is,balancing the needs for strength, clarity, temperature resistance,surface energy, adherence to the optical layer, among others. Thethickness of the base layer is typically at least about 0.025millimeters (mm) and more typically at least about 0.125 mm. Further,the base layer generally has a thickness of no more than about 1 mm.

Useful base layer and/or microstructured optical layer materials includeglass and various polymeric materials including cellulose acetatebutyrate, cellulose acetate propionate, cellulose triacetate, polyethersulfone, polymethyl methacrylate, polyurethane, polyester,polycarbonate, polyvinyl chloride, syndiotactic polystyrene,polyethylene naphthalate, norbornene polymers, copolymers or blendsbased on naphthalene dicarboxylic acids. Optionally, the base materialcan contain mixtures or combinations of these materials. For example,the base may be multi-layered or may contain a dispersed phase suspendedor dispersed in a continuous phase. Exemplary base layer materialsinclude polyethylene terephthalate (PET) and polycarbonate. Examples ofuseful PET films include photograde polyethylene terephthalate (PET) andPET commercially available from DuPont Films of Wilmington, Del., underthe trade designation “Melinex”.

Films produced from such base layer materials typically have somebirefringence as a result of the film manufacturing process. Althoughmicrostructured optical films prepared from such base layers would alsohave such birefringence, such films are typically not characterized aspolarizing films, since such optical films would not be employed as apolarizer in an illuminated (e.g. LCD) display. As used herein,“substantially non-polarizing optical film” refers to optical filmswhose diffuse reflectance varies by less than 0.5 as a function ofpolarization. Further, it is also common for a film (e.g. that isstretched during manufacturing) to have a higher index of refraction inone axis (e.g. machine direction) in comparison to a different axis(e.g. cross web direction).

In contrast “reflective polarizing optical film” refers to optical filmswhose diffuse reflectance varies by at least 0.05 as a function ofpolarization. Reflective polarizing optical films typically have asubstantially higher reflectivity for one polarization mode than foranother. Typically, the diffuse reflectance varies by at least 0.1 andmore typically by at least 0.2 as a function of polarization.

Microstructured reflective polarizing optical films can be manufacturedfrom a base layer material that is optically active, and can act as apolarizing material. A number of base layer materials are known to beuseful as polarizing materials. Light polarization can also be achievedby including inorganic materials such as aligned mica chips or by adiscontinuous phase dispersed within a continuous film, such as dropletsof light modulating liquid crystals dispersed within a continuous film.As an alternative, a film can be prepared from microfine layers ofdifferent materials. The polarizing materials within the film can bealigned into a polarizing orientation, for example, by employing methodssuch as stretching the film, applying electric or magnetic fields, andcoating techniques.

Examples of polarizing films include those described in U.S. Pat. Nos.5,825,543 and 5,783,120. Multilayer polarizing films are sold by 3MCompany, St. Paul, Minn. under the trade designation DBEF (DualBrightness Enhancement Film). The use of such multilayer polarizingoptical film in a brightness enhancement film has been described in U.S.Pat. No. 5,828,488; incorporated herein by reference. Other examples ofpolarizing films are described in U.S. Pat. Nos. 5,882,774, 5,965,247,6,025,897. Other polarizing and non-polarizing films can also be usefulas the base layer for brightness enhancing films of the invention suchas described in U.S. Pat. Nos. 5,612,820 and 5,486,949, among others.

In some embodiments, unstructured polarizing and substantiallynon-polarizing films may be employed as the base layer of themicrostructured optical film. In other embodiments, unstructuredpolarizing and substantially non-polarizing films are employed in anassembly in combination with at least one microstructured optical film.As used herein “unstructured polarizing films” refers to films that lacka (e.g. prismatic) surface structure. Unstructured polarizing films mayhave smooth, matte, or rough surface.

Brightness enhancing films generally enhance on-axis luminance (referredherein as “brightness”) of a lighting device. When used in an opticaldisplay such as that found in laptop computers, watches, etc., themicrostructured optical film can increase brightness of an opticaldisplay by limiting light escaping from the display to within a pair ofplanes disposed at desired angles from a normal axis running through theoptical display. As a result, light that would exit the display outsideof the allowable range is reflected back into the display where aportion of it can be “recycled” and returned back to the microstructuredfilm at an angle that allows it to escape from the display. Therecycling is useful because it can reduce power consumption needed toprovide a display with a desired level of brightness.

A common way of measuring the effectiveness of such recycling of lightis to measure the gain of an optical film. As used herein, “relativegain”, is defined as the on-axis luminance, as measured by the testmethod described in the examples, when an optical film (or optical filmassembly) is placed on top of the light box, relative to the on-axisluminance measured when no optical film is present on top of the lightbox. This definition can be summarized by the following relationship:Relative Gain=(Luminance measured with optical film)/(Luminance Measuredwithout Optical Film)

Presently described are optical films and optical film assembliesexhibiting higher relative gain.

In one embodiment, an optical film comprising a light transmissive (e.g.cured) polymeric material having a microstructured surface is described.The optical film is a substantially non-polarizing film having a singlesheet relative gain of at least 1.78. The relative single sheet gain istypically no greater than 2.05. Accordingly, the single sheet relativegain may also range from any values in the set of relative gain valuesincluding 1.80, 1.82, 1.84, 1.86, 1.88, 1.90, 1.92, 1.94, 1.96, 1.98,2.00, and 2.02.

In another embodiment, a reflective polarizing optical film having amicrostructured surface is described wherein the film comprises a lighttransmissive (e.g. cured) polymeric material and has a single sheetrelative gain of at least 2.46. The relative single sheet gain istypically less than 3.02. Accordingly, the single sheet relative gainmay also range from any values in the set of relative gain valuesincluding 2.48, 2.50, 2.52, 2.54, 2.56, 2.58, 2.60, 2.62, 2.64, 2.66,2.68, 2.70, 2.72, 2.74, 2.76, 2.78, 2.80, 2.82, 2.84, 2.86, 2.88, 2.90,2.92, 2.94, 2.96, 2.98, and 3.00. When a reflective polarizing film isemployed as a base layer in a (e.g. prismatic) microstructured opticalfilm, it is preferred that the (e.g. linear) prisms or grooves arealigned in a direction substantially orthogonal to the pass axis of thereflective polarizing film.

In other embodiments, the inventions relate to various assemblies thatcomprise or consist of two or more films. Each assembly includes a firstmicrostructured optical film proximate a second (e.g. microstructured orunstructured) optical film.

By proximate, it is meant sufficiently near. Proximate can include thefirst microstructured optical film being in contact with the secondoptical film such as by the films merely being stacked together or thefilms may be attached by various means. The films may be attached bymechanical means, chemical means, thermal means, or a combinationthereof. Chemical means includes various pressure sensitive,solvent-based, and hot melt adhesives as well as two-part curableadhesive compositions that crosslink upon exposure to heat, moisture, orradiation. Thermal means includes for example a heated embossed roller,radio frequency (RF) welding, and ultrasonic welding. The optical filmsmay be attached (e.g. continuously) across the entire plane of thefilms, at only select points, or at only the edges. Alternatively, theproximate optical films may be separated from each other with an airinterface. The air interface may be created by increasing the thicknessof either or both optical films at the periphery, such as by applicationof an adhesive. When the films are stacked rather than laminatedtogether, the air interface between the optical films may be only a fewmicrons.

In some embodiments, a first microstructured optical film is proximate asecond microstructured optical film. In such assemblies, themicrostructured surface of the bottom film is preferably disposedproximate the unstructured surface of the top film. For embodiments thatemploy prismatic microstructured films, the prisms of the films aregenerally aligned parallel in one principal direction, the prisms beingseparated by grooves. It is generally preferred to align the prisms (orgrooves) of the second (e.g. bottom) microstructured optical film in astack such that the prisms are substantially orthogonal to the prisms ofthe first (e.g. top) film. However, other alignments can also beemployed. For example, the prisms of the second optical film may bepositioned relative to the prisms of the second optical film such thatthe intersection of grooves or prisms form angles ranging from about 70°to about 120°.

In one embodied assembly, a first microstructured substantiallynon-polarizing optical film is proximate a second microstructuredsubstantially non-polarizing optical film. The gain of this assembly isat least 2.80. The first optical film may be the same as or differentthan the second optical film. For example, the second film may have adifferent base layer composition, a different microstructured surfacecomposition, and/or may have a different surface microstructure. Therelative gain of this assembly is typically less than 3.32. Accordingly,the relative gain of such assembly may also range from any values in theset of relative gain values including 2.81, 2.82, 2.84, 2.86, 2.88,2.90, 2.92, 2.94, 2.96, 2.98, 3.00, 3.02, 3.04, 3.06, 3.08, 3.10, 3.12,3.14, 3.16, 3.18, 3.20, 3.22, 3.24, 3.26, 3.28, and 3.30.

Reflective polarizing optical films can be combined with other opticalfilms in various assemblies. Such combinations are especially useful forenhancing the output of a diffuse light source with respect to aspecific light direction and polarization mode, and are particularlyuseful for brightness enhancement in liquid crystal devices.

In one embodied assembly, a first (e.g. prismatic) microstructuredsubstantially non-polarizing optical film is proximate a non-structuredreflective polarizing film. The gain of this assembly is at least 2.59.The relative gain of this assembly is typically less than 2.86.Accordingly, the relative gain of such assembly may also range from anyvalues in the set of relative gain values including 2.60, 2.62, 2.64,2.66, 2.68, 2.70, 2.72, 2.74, 2.76, 2.78, 2.80, 2.82, and 2.84. In suchan assembly, it is preferred that the prisms or grooves of the prismaticfilm are aligned substantially orthogonal to the pass axis of thenon-structured reflective polarizing film.

In another embodied assembly, a first microstructured substantiallynon-polarizing optical film is proximate a microstructured reflectivepolarizing film. The relative gain of this assembly is typically atleast 3.33. Further, the relative gain is typically less than 4.20.Accordingly, the relative gain of such assembly may also range from anyvalues in the set of relative gain values including 3.34, 3.36, 3.38,3.40, 3.42, 3.44, 3.46, 3.48, 3.50, 3.52, 3.54, 3.56, 3.58, 3.60, 3.62,3.64, 3.66, 3.68, 3.70, 3.72, 3.74, 3.76, 3.78, 3.80, 3.82, 3.84, 3.86,3.88, 3.90, 3.82, 3.94, 3.96, 3.98, 4.00, 4.02, 4.04, 4.06, 4.08, 4.10,4.12, 4.14, 4.16, and 4.18.

The various assemblies of microstructured optical films can further becombined with a third optical film. Typically, however, the assemblycomprises no greater than two microstructured films with prismaticstructures proximate each other. One preferred assembly includes a firstand second microstructured substantially non-polarizing optical filmproximate each other with a non-structured reflective polarizing opticalfilm. The reflective polarizing film is generally disposed adjacent theassembly of non-reflective polarizing films. During use, the stack ispositioned in a display device such that the reflective polarizing filmis father from the light source. The relative gain of this three layerstack is typically at least 3.40 and typically no greater than 3.72.Alternatively, however, the non-structured reflective polarizing opticalfilm may be placed between or below the first and second microstructuredsubstantially non-polarizing films.

It is known from electromagnetic theory that refractive index and axialgain are generally directly related. Accordingly, there are variouspatents directed to higher refractive index material for use inbrightness enhancing films. However, the present inventors havediscovered that high-index materials alone do not necessarily providehigher gain, particularly in an assembly. Presently described areoptical films and assemblies of two or more optical films prepared frompolymerizable resins having a synergistic combination of sufficientrefractive index and low optical absorption.

The refractive index, as determined with a Fischer ScientificRefractometer Co. Model # 6208, of the organic component of thepolymerizable composition may be at least 1.48, 1.49, 1.50, 1.51, 1.52,1.53, 1.54, 1.55, 1.56, 1.57, 1.58, 1.59, 1.60 1.61, or 1.62. Thepolymerizable composition (e.g. optionally including particles) can havea refractive index as high as 1.70. The refractive index of thepolymerizable composition is at least 1.58, 1.59, 1.60, 1.61, 1.62,1.63, 1.64, 1.65, 1.66, 1.67, 1.68, or 1.69. In general, the refractiveindices of the resins may rise upon curing by approximately 0.01 to0.03. Cured refractive indices can be measured by various techniques asknown in the art, such as ellipsometry.

FIG. 3 is a plot of absorbance (as measured according to the test methoddescribed in the example) as a function of wavelength of representativepolymerizable resin compositions (i.e. Polymerizable Resin Compositions12 and 13 of the examples) employed to produce a substantiallynon-polarizing microstructured optical film having (i.e. single sheet)relative gain values of 1.793 and 1.829 respectively. PolymerizableComposition 12 is thus representative of a composition suitable forproducing a microstructured optical film having a (i.e. single sheet)relative gain value near the preferred minimum value of 1.78.

As can be seen by FIG. 3, the absorbance of these polymerizable resincompositions at wavelengths ranging from about 575 nm to 800 nm is lessthan 1. The absorbance at 450 nm is less than 2.5 (e.g. less than 2.25).The absorbance at about 500 nm is no greater than 1.75. The absorbanceat 550 nm is less than 1.5 (e.g. less than 1.25).

The substantially non-polarizing microstructured optical films producedfrom representative Polymerizable Resin 12 and 13 were prepared intoassemblies each having a stack of two of the same films wherein theprismatic microstructured surface of the bottom film was contacted withthe base layer of the top film such that the prisms of the bottom filmwere orthogonal with the prisms of the top film. The relative gain ofthe assembly produced from Polymerizable Resin 12 was 2.652; whereas therelative gain of the assembly produced from Polymerizable Resin 13 was2.807.

Although Polymerizable Resin 12 has sufficiently low absorbance toobtain a single microstructured optical film having a high gain, whencombined into an assembly the absorbance contributed by thepolymerizable resin is compounded. Thus, in the assemblies of theinvention, representative Polymerizable Resin 12 has too high of anabsorbance; whereas Polymerizable Resin 13 is a representativecomposition having an absorbance near the maximum absorbance that issuitable for producing an assembly (i.e. lacking a reflective polarizingfilm) having the preferred gain value of at least 2.80.

Accordingly, the absorbance of preferred polymerizable resincompositions for use in assemblies is less than 2 at a wavelength of 450nm. Preferably the absorbance is less than 1.5, more preferably lessthan 1 and even more preferably less than 0.75 at a wavelength of 450nm. The absorbance at about 500 nm is preferably less than 1.5, morepreferably less than 1.0, and more preferably less than 0.5. At awavelength of about 550 nm, the absorbance of the polymerizable resin ispreferably less than 1 and more preferably less than 0.5. At wavelengthbetween 500 nm and 800 nm, the absorbance of the polymerizable resin ispreferably less than 0.5. The absorbance is preferably less than 0.25 atwavelengths ranging from about 600 nm to 800 nm.

The effect of absorbance on relative gain can be compensated to someextent by use of a polymerizable resin composition having a higherrefractive index (e.g. 1.64). In such embodiment, the allowableabsorbance values may be higher.

The various microstructured optical films and assemblies describedherein can usefully be employed in a variety of displays including forexample, direct lit backlights, edge lit backlights, light emittingdiode (LED) back lit LCD's, CCFL back lit displays, field-sequentialdisplays, scanning backlights. The microstructured optical film orassembly is typically included to improving the brightness and/orlowering the power consumption. The microstructured optical film(s) orassembly is proximate the other components of the display device. Aschematic view of an illustrative backlit liquid crystal display isgenerally indicated at 110 in FIG. 2. In the actual display, the variouscomponents depicted are often in contact with the brightness enhancingfilm. The brightness enhancing film 111 of the present invention isgenerally positioned between a light guide 118 and a liquid crystaldisplay panel 114. The liquid crystal display panel typically includesan (e.g. absorbing) polarizer on both surfaces. Thus, such (e.g.absorbing) polarizer is positioned adjacent to the brightness enhancingfilm of the invention. In the display device the prisms or grooves ofthe prism sheet closest to the (e.g. absorbing) polarizer are preferablyaligned substantially orthogonal to the pass axis of the adjacentabsorbing polarizer. Further, when the optical film or assembly includesa reflective polarizer, the pass axis of the reflective polarizer isaligned with the pass axis of the absorbing polarizer of the displaydevice. The backlit liquid crystal display can also include a lightsource 116 such as a fluorescent lamp and a white reflector 120 also forreflecting light toward the liquid crystal display panel. The brightnessenhancing film 111 collimates light emitted from the light guide 118thereby increasing the brightness of the liquid crystal display panel114. The increased brightness enables a sharper image to be produced bythe liquid crystal display panel and allows the power of the lightsource 116 to be reduced to produce a selected brightness. The backlitliquid crystal display is useful in equipment such as computer displays(laptop displays and computer monitors), televisions, video recorders,mobile communication devices, handheld devices (i.e. cell phone,personal digital assistant (PDA)), automobile and avionic instrumentdisplays, and the like, represented by reference character 121.

The display may further include another optical film 112 positionedbetween the brightness enhancing film and the liquid crystal displaypanel 114. The other optical film may include for example a diffuser, areflective polarizer, or a second brightness enhancing film. Otheroptical films may be positioned between optical film 112 and the liquidcrystal display panel 114 or between the brightness enhancing film 111and the light guide 118, as are known in the art. Further, a turningfilm may be located between lightguide and optical film. Alternatively,the brightness enhancing film may be a turning film. A turning filmtypically includes prism structures formed on an input surface, and theinput surface is disposed adjacent the lightguide. The light raysexiting the lightguide at the glancing angle, usually less than 30degrees to the output surface, encounter the prism structures. The lightrays are refracted by a first surface of the prism structures and arereflected by a second surface of the prism structures such that they aredirected by the turning lens or film in the desired direction, e.g.,substantially parallel to a viewing axis of the display.

The combination of 111 and 112 alone or in combination with a thirdoptical film may be any of the optical film assemblies described herein.If these additional optical films are included as the base layer of thebrightness enhancing films, then the thickness of the base layer may beconsiderably greater than previously described.

In one preferred aspect, a microstructured non-polarizing film or anassembly including such has been found to improve the on-axis luminanceof certain backlights. Off-axis luminance peaks have been found to becommon in edge-lit backlight displays including specular backreflectors, and particularly in such displays including a wedgelightguide.

The optical films described herein can comprise a polymerized structurecomprising the reaction product of an organic component optionallycomprising a plurality of (e.g. surface modified) nanoparticles. Thepolymerized structure can be an optical element or optical productconstructed of a base layer and an optical layer. The base layer andoptical layer can be formed from the same or different polymer material.

As described in Lu (U.S. Pat. No. 5,183,597) and Lu et al. (U.S. Pat.No. 5,175,030), a microstructure-bearing article (e.g. brightnessenhancing film) can be prepared by a method including the steps of (a)preparing a polymerizable composition (i.e. the polymerizablecomposition of the invention); (b) depositing the polymerizablecomposition onto a master negative microstructured molding surface in anamount barely sufficient to fill the cavities of the master; (c) fillingthe cavities by moving a bead of the polymerizable composition between apreformed base and the master, at least one of which is flexible; and(d) curing the composition. The master can be metallic, such as nickel,nickel-plated copper or brass, or can be a thermoplastic material thatis stable under the polymerization conditions, and that preferably has asurface energy that allows clean removal of the polymerized materialfrom the master. One or more the surfaces of the base film can beoptionally be primed or otherwise be treated to promote adhesion of theoptical layer to the base.

Suitable methods of polymerization include solution polymerization,suspension polymerization, emulsion polymerization, and bulkpolymerization, as are known in the art. Suitable methods includeheating in the presence of a free-radical initiator as well asirradiation with electromagnetic radiation such as ultraviolet orvisible light in the presence of a photoinitiator. Inhibitors such ashydroquinone, 4-methoxy phenol, and hindered amine nitroxide inhibitorsat levels of 50-1000 ppm are frequently used in the synthesis of thepolymerizable composition to prevent premature polymerization of theresin during synthesis, transportation and storage. Other kinds and/oramounts of inhibitors may be employed as known to those skilled in theart. The composition of the invention is preferably polymerizable byirradiation with ultraviolet or visible light in the presence of aphotoinitiator.

The polymerizable composition or organic component thereof is preferablya substantially solvent free polymerizable composition. “Substantiallysolvent free” refer to the polymerizable composition having less than 5wt-%, 4 wt-%, 3 wt-%, 2 wt-%, 1 wt-%, and 0.5 wt-% of (e.g. organic)solvent. The concentration of solvent can be determined by knownmethods, such as gas chromatography. Solvent concentrations of less than0.5 wt-% are preferred.

The organic component can be a solid or comprise a solid componentprovided that the melting point in the polymerizable composition is lessthan the coating temperature. The organic component can be a liquid atambient temperature.

The components are preferably chosen such that the organic component hasa low viscosity, such as less than 1000 cps at 180° F. Typically theviscosity of the organic component is substantially lower than theorganic component of compositions previously employed. The viscosity ofthe organic component is less than 1000 cps and typically less than 900cps. The viscosity of the organic component may be less than 800 cps,less than 450 cps, less than 600 cps, or less than 500 cps at thecoating temperature. As used herein, viscosity is measured with 25 mmparallel plates using a Dynamic Stress Rheometer (at a shear rate up to1000 sec-1). Further, the viscosity of the organic component istypically at least 10 cps, more typically at least 50 cps, even moretypically at least 100 cps, and most typically at least 200 cps at thecoating temperature. The coating temperature typically ranges fromambient temperature, (i.e. 25° C.) to 180° F. (82° C.). The coatingtemperature may be less than 170° F. (77° C.), less than 160° F. (71°C.), less than 150° F. (66° C.), less than 140° F. (60° C.), less than130° F. (54° C.), or less than 120° F. (49° C.).

The polymerizable composition comprises one or more ethylenicallyunsaturated monomers. The polymerizable composition may comprise a(meth)acrylated urethane oligomer, a (meth)acrylated polyester oligomer,a (meth)acrylated phenolic oligomer, a (meth)acrylated acrylic oligomer,and mixtures thereof. In some embodiments, however, the organiccomponent is free of urethane linkages and thus prepared from thereaction product of a polymerizable composition that is free of(meth)acrylated urethane. Polymerizable compositions comprising(meth)acrylated urethanes tend to be higher in viscosity.

In some embodiments, the polymerizable composition may comprise at leastone oligomeric ethylenically unsaturated monomer having a number averagemolecular weight of greater than 450 g/mole in combination with areactive diluent and/or crosslinker. In other embodiments, thepolymerizable composition may comprise one or more ethylenicallyunsaturated monomers wherein the organic phase is free of oligomericmonomer having a number average molecular weight of greater than 450g/mole.

For embodiments wherein surface modified nanoparticles having sufficientpolymerizable reactive groups are employed, a crosslinking agent neednot be employed. In preferred embodiments the polymerizable compositionand thus components thereof comprises solely acrylate functionality andthus is substantially free of methacrylate functional groups.

The polymerizable composition described herein preferably comprises(e.g. surface modified) inorganic oxide particles. The size of suchparticles is chosen to avoid significant visible light scattering. Itmay be desirable employ a mixture of inorganic oxide particle types tooptimize an optical or material property and to lower total compositioncost. Hybrid polymers formed from inorganic nanoparticles and organicresin is amenable to achieving durability unobtainable with conventionalorganic resins alone. The inclusion of the inorganic nanoparticles canimprove the durability of the articles (e.g. brightness enhancing film)thus formed.

Although inorganic nanoparticles lacking polymerizable surfacemodification can usefully be employed, the inorganic nanoparticles arepreferably surface modified such that the nanoparticles arepolymerizable with the organic component. Surface modified (e.g.colloidal) nanoparticles can be present in the polymerized structure inan amount effective to enhance the durability and/or refractive index ofthe article or optical element. The surface modified colloidalnanoparticles described herein can have a variety of desirableattributes, including for example; nanoparticle compatibility with resinsystems such that the nanoparticles form stable dispersions within theresin systems, surface modification can provide reactivity of thenanoparticle with the resin system making the composite more durable,properly surface modified nanoparticles added to resin systems provide alow impact on uncured composition viscosity. A combination of surfacemodifiers can be used to manipulate the uncured and cured properties ofthe composition. Appropriately surface modified nanoparticles canimprove the optical and physical properties of the optical element suchas, for example, improve resin mechanical strength, minimize viscositychanges while increasing solid volume loading in the resin system andmaintain optical clarity while increasing solid volume loading in theresin system.

The surface modified colloidal nanoparticles can be oxide particleshaving a primary particle size or associated particle size of greaterthan 1 nm and less than 100 nm. It is preferred that the nanoparticlesare unassociated. Their measurements can be based on transmissionelectron microscopy (TEM). The nanoparticles can include metal oxidessuch as, for example, alumina, tin oxides, antimony oxides, silica,zirconia, titania, mixtures thereof, or mixed oxides thereof. Surfacemodified colloidal nanoparticles can be substantially fully condensed.

Non-silica containing fully condensed nanoparticles typically have adegree of crystallinity (measured as isolated metal oxide particles)greater than 55%, preferably greater than 60%, and more preferablygreater than 70%. For example, the degree of crystallinity can range upto about 86% or greater. The degree of crystallinity can be determinedby X-ray defraction techniques. Condensed crystalline (e.g. zirconia)nanoparticles have a high refractive index whereas amorphousnanoparticles typically have a lower refractive index.

Silica nanoparticles can have a particle size from 5 to 75 nm or 10 to30 nm or 20 nm. Silica nanoparticles can be present in the durablearticle or optical element in an amount from 10 to 60 wt-%, or 10 to 40wt-%. Silicas for use in the materials of the invention are commerciallyavailable from Nalco Chemical Co., Naperville, Ill. under the tradedesignation “Nalco Collodial Silicas” such as products 1040, 1042, 1050,1060, 2327 and 2329. Suitable fumed silicas include for example,products commercially available from DeGussa AG, (Hanau, Germany) underthe trade designation, “Aerosil series OX-50”, as well as productnumbers -130, -150, and -200. Fumed silicas are also commerciallyavailable from Cabot Corp., Tuscola, I, under the trade designationsCAB-O-SPERSE 2095”, “CAB-O-SPERSE A105”, and “CAB-O-SIL M5”.

Zirconia nanoparticles can have a particle size from 5 to 50 nm, or 5 to15 nm, or 10 nm. Zirconia nanoparticles can be present in the durablearticle or optical element in an amount from 10 to 70 wt-%, or 30 to 60wt-%. Zirconias for use in composition and articles of the invention areavailable from Nalco Chemical Co. under the trade designation “NalcoOOSSOO8” and from Buhler AG Uzwil, Switzerland under the tradedesignation “Buhler zirconia Z-WO sol”. Zirconia nanoparticle can alsobe prepared such as described in U.S. Pat. Nos. 6,376,590 and 7,241,437.

Titania, antimony oxides, alumina, tin oxides, and/or mixed metal oxidenanoparticles can have a particle size or associated particle size from5 to 50 nm, or 5 to 15 nm, or 10 nm. Titania, antimony oxides, alumina,tin oxides, and/or mixed metal oxide nanoparticles can be present in thedurable article or optical element in an amount from 10 to 70 wt-%, or30 to 60 wt-%. Mixed metal oxide for use in materials of the inventionare commercially available from Catalysts & Chemical Industries Corp.,Kawasaki, Japan, under the trade designation “Optolake 3”.

Surface-treating the nano-sized particles can provide a stabledispersion in the polymeric resin. Preferably, the surface-treatmentstabilizes the nanoparticles so that the particles will be welldispersed in the polymerizable resin and results in a substantiallyhomogeneous composition. Furthermore, the nanoparticles can be modifiedover at least a portion of its surface with a surface treatment agent sothat the stabilized particle can copolymerize or react with thepolymerizable resin during curing.

The nanoparticles of the present invention are preferably treated with asurface treatment agent. In general a surface treatment agent has afirst end that will attach to the particle surface (covalently,ionically or through strong physisorption) and a second end that impartscompatibility of the particle with the resin and/or reacts with resinduring curing. Examples of surface treatment agents include alcohols,amines, carboxylic acids, sulfonic acids, phosphonic acids, silanes andtitanates. The preferred type of treatment agent is determined, in part,by the chemical nature of the metal oxide surface. Silanes are preferredfor silica and other for siliceous fillers. Silanes and carboxylic acidsare preferred for metal oxides such as zirconia. The surfacemodification can be done either subsequent to mixing with the monomersor after mixing. It is preferred in the case of silanes to react thesilanes with the particle or nanoparticle surface before incorporationinto the resin. The required amount of surface modifier is dependantupon several factors such particle size, particle type, modifiermolecular wt, and modifier type. In general it is preferred thatapproximately a monolayer of modifier is attached to the surface of theparticle. The attachment procedure or reaction conditions required alsodepend on the surface modifier used. For silanes it is preferred tosurface treat at elevated temperatures under acidic or basic conditionsfor from 1-24 hr approximately. Surface treatment agents such ascarboxylic acids may not require elevated temperatures or extended time.

Representative embodiments of surface treatment agents suitable for thecompositions include compounds such as, for example, isooctyltrimethoxy-silane, N-(3-triethoxysilylpropyl) methoxyethoxyethoxyethylcarbamate, N-(3-triethoxysilylpropyl) methoxyethoxyethoxyethylcarbamate, 3-(methacryloyloxy)propyltrimethoxysilane,3-acryloxypropyltrimethoxysilane,3-(methacryloyloxy)propyltriethoxysilane, 3-(methacryloyloxy)propylmethyldimethoxysilane, 3-(acryloyloxypropyl)methyldimethoxysilane,3-(methacryloyloxy)propyldimethylethoxysilane, 3-(methacryloyloxy)propyldimethylethoxysilane, vinyldimethylethoxysilane,phenyltrimethoxysilane, n-octyltrimethoxysilane,dodecyltrimethoxysilane, octadecyltrimethoxysilane,propyltrimethoxysilane, hexyltrimethoxysilane,vinylmethyldiacetoxysilane, vinylmethyldiethoxysilane,vinyltriacetoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane,vinyltrimethoxysilane, vinyltriphenoxysilane, vinyltri-t-butoxysilane,vinyltris-isobutoxysilane, vinyltriisopropenoxysilane,vinyltris(2-methoxyethoxy)silane, styrylethyltrimethoxysilane,mercaptopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane,acrylic acid, methacrylic acid, oleic acid, stearic acid, dodecanoicacid, 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA),beta-carboxyethylacrylate (BCEA), 2-(2-methoxyethoxy)acetic acid,methoxyphenyl acetic acid, and mixtures thereof. Further, a proprietarysilane surface modifier, commercially available from OSI Specialties,Crompton South Charleston, W. Va. under the trade designation “SilquestA1230”, has been found particularly suitable.

The surface modification of the particles in the colloidal dispersioncan be accomplished in a variety of ways. The process involves themixture of an inorganic dispersion with surface modifying agents.Optionally, a co-solvent can be added at this point, such as forexample, 1-methoxy-2-propanol, ethanol, isopropanol, ethylene glycol,N,N-dimethylacetamide and 1-methyl-2-pyrrolidinone. The co-solvent canenhance the solubility of the surface modifying agents as well as thesurface modified particles. The mixture comprising the inorganic sol andsurface modifying agents is subsequently reacted at room or an elevatedtemperature, with or without mixing. In a preferred method, the mixturecan be reacted at about 85° C. for about 24 hours, resulting in thesurface modified sol. In a preferred method, where metal oxides aresurface modified the surface treatment of the metal oxide can preferablyinvolve the adsorption of acidic molecules to the particle surface. Thesurface modification of the heavy metal oxide may take place at roomtemperature.

The surface modification of ZrO₂ with silanes can be accomplished underacidic conditions or basic conditions. In one preferred case the silanesare preferably heated under acid conditions for a suitable period oftime. At which time the dispersion is combined with aqueous ammonia (orother base). This method allows removal of the acid counter ion from theZrO₂ surface as well as reaction with the silane. In a preferred methodthe particles are precipitated from the dispersion and separated fromthe liquid phase.

The surface modified particles can then be incorporated into the curableresin in various methods. In a preferred aspect, a solvent exchangeprocedure is utilized whereby the resin is added to the surface modifiedsol, followed by removal of the water and co-solvent (if used) viaevaporation, thus leaving the particles dispersed in the polymerizableresin. The evaporation step can be accomplished for example, viadistillation, rotary evaporation or oven drying.

In another aspect, the surface modified particles can be extracted intoa water immiscible solvent followed by solvent exchange, if so desired.

Alternatively, another method for incorporating the surface modifiednanoparticles in the polymerizable resin involves the drying of themodified particles into a powder, followed by the addition of the resinmaterial into which the particles are dispersed. The drying step in thismethod can be accomplished by conventional means suitable for thesystem, such as, for example, oven drying or spray drying.

A combination of surface modifying agents can be useful, wherein atleast one of the agents has a functional group co-polymerizable with ahardenable resin. Combinations of surface modifying agent can result inlower viscosity. For example, the polymerizing group can beethylenically unsaturated or a cyclic function subject to ring openingpolymerization. An ethylenically unsaturated polymerizing group can be,for example, an acrylate or methacrylate, or vinyl group. A cyclicfunctional group subject to ring opening polymerization generallycontains a heteroatom such as oxygen, sulfur or nitrogen, and preferablya 3-membered ring containing oxygen such as an epoxide.

A preferred combination of surface modifying agent includes at least onesurface modifying agent having a functional group that isco-polymerizable with the (organic component of the) hardenable resinand a second modifying agent different than the first modifying agent.The second modifying agent is optionally co-polymerizable with theorganic component of the polymerizable composition. The second modifyingagent may have a low refractive index (i.e. less than 1.52 or less than1.50). The second modifying agent is preferably a polyalkyleneoxidecontaining modifying agent that is optionally co-polymerizable with theorganic component of the polymerizable composition.

A variety of ethylenically unsaturated monomer may be employed in theorganic component of the polymerizable composition.

Suitable oligomeric (meth)acrylated aromatic epoxy oligomers arecommercially available from Sartomer under the trade designations“CN104”, “CN116”, “CN120”, CN121” and “CN136”; from Cognis under thetrade designation “Photomer 3016”; and from UCB under the tradedesignations “3200”, “3201”, “3211” and “3212”.

Suitable urethane (meth)acrylates are commercially available fromSartomer under the trade designations “CN965”, “CN968”, “CN981”, “CN983”, “CN 984”, “CN972”, and “CN978”; from Cognis under the tradedesignation “Photomer 6210”, “Photomer 6217”, “Photomer 6230”, “Photomer6623”, “Photomer 6891”, and “Photomer 6892”; and from UCB under thetrade designations “Ebecryl 1290”, “Ebecryl 2001”, and “Ebecryl 4842”.

Suitable polyester (meth)acrylates are commercially available fromSartomer under the trade designation “CN292”; from Cognis under thetrade designation “Photomer 5010”, “Photomer 5429”, “Photomer 5430”,“Photomer 5432”, “Photomer 5662”, “Photomer 5806”, and “Photomer 5920”;and from UCB under the trade designations “Ebecryl 80”, “Ebecryl 81”,“Ebecryl 83”, “Ebecryl 450”, “Ebecryl 524”, “Ebecryl 525”, “Ebecryl585”, “Ebecryl 588”, “Ebecryl 810”, and “Ebecryl 2047”.

Suitable phenolic (meth)acrylates are commercially available fromSartomer under the trade designation “SR601” and “SR602”; from Cognisunder the trade designations “Photomer 4025” and “Photomer 4028”.

Suitable (meth)acrylated acrylic oligomers are also commerciallyavailable or can be prepared by methods know in the art.

The polymerizable composition may comprise a first monomer thatcomprises a major portion having the following general structures I orII:

In each of structures I and II, each R1 is independently hydrogen ormethyl. Each R2 is independently hydrogen or bromine. Each Z isindependently —C(CH₃)₂—, —CH₂—, —C(O)—, —S—, —S(O)—, or —S(O)₂—, andeach Q is independently O or S. Typically, the R1 groups are the same.Typically, the R2 groups are the same as each other well. In structureII, L is a linking group. L may independently comprise a branched orlinear C₂-C₁₂ alkyl group. The carbon chain of the alkyl group mayoptionally be substituted with one or more oxygen groups. Further, thecarbon atoms of the alkyl group may optionally be substituted with oneor more hydroxyl groups. For example L may be —CH₂CH(OH)CH₂—. Typically,the linking groups are the same. Preferably the alkyl group comprises nomore than 8 carbon atoms and more preferably no more than 6 carbonatoms. Mixtures of I and II may also be employed.

The first monomer may be synthesized or purchased. As used herein, majorportion refers to at least 60-70 wt-% of the monomer containing thespecific structure(s) just described. It is commonly appreciated thatother reaction products are also typically present as a byproduct of thesynthesis of such monomers.

The first monomer is preferably the reaction product ofTetrabromobisphenol A diglycidyl ether and acrylic acid. The firstmonomer may be obtained from UCB Corporation, Smyrna, Ga. under thetrade designation “RDX-51027”. This material comprises a major portionof 2-propenoic acid,(1-methylethylidene)bis[(2,6-dibromo-4,1-phenylene)oxy(2-hydroxy-3,1-propanediyl)]ester.

Although, mixtures of such first monomers may also suitably be employed,for ease in manufacturing it is preferred to employ as few differentmonomers as possible, yet still attain a brightness enhancing film withsuitable gain. To meet this end, it is preferred that the brightnessenhancing film is comprised of the reaction product of only one of thesefirst monomers and in particular the reaction product ofTetrabromobisphenol A diglycidyl ether and acrylic acid.

The polymerizable composition may comprise at least one (meth)acrylatedaromatic epoxy oligomer. Various (meth)acrylated aromatic epoxyoligomers are commercially available. For example, (meth)acrylatedaromatic epoxy, (described as a modified epoxy acrylates), are availablefrom Sartomer, Exton, Pa. under the trade designation “CN118”, “CN115”and “CN112C60”. (Meth)acrylated aromatic epoxy oligomer, (described asan epoxy acrylate oligomer), is available from Sartomer under the tradedesignation “CN2204”. Further, an (meth)acrylated aromatic epoxyoligomer, (described as an epoxy novolak acrylate blended with 40%trimethylolpropane triacrylate), is available from Sartomer under thetrade designation “CN112C60”.

In some embodiments, the aromatic epoxy acrylate is derived frombisphenol A, such as those of II. In other embodiments, however, thearomatic epoxy acrylate may be derived from a monomer different thanbisphenol A.

The polymerizable composition component may comprise aromatic epoxyacrylate, at least one crosslinking agent, at least one reactivediluent, and at least one other ethylenically unsaturated monomer.Alternatively, the organic component of the polymerizable compositionmay only include the aromatic epoxy acrylate and crosslinking agent orthe aromatic epoxy acrylate and reactive diluent, each of such includingphotoinitiator. If an aromatic epoxy acrylate is employed thepolymerizable composition, the aromatic epoxy acrylate may bemonofunctional provided that the polymerizable composition includes atleast one ingredient that comprises at least two ethylenicallyunsaturated polymerizable groups. The aromatic epoxy acrylate may havethree or more (meth)acrylate groups. The aromatic epoxy (meth)acrylatemay be halogenated, typically having a refractive index of greater than1.56. In other aspects, the aromatic epoxy (meth)acrylate may have arefractive index of less than 1.56. The aromatic epoxy (meth)acrylatemay have a viscosity of greater than 2150 cps at 65° C. Less than 30wt-% of the aromatic epoxy (meth)acrylate may be employed, for examplein combination with a reactive diluent. In other embodiments, thearomatic epoxy (meth)acrylate may have a viscosity of less than 2150 cpsat 65° C., and diluent may not be employed. Greater than 30 wt-% of thearomatic epoxy (meth)acrylate may be employed in organic component.

The first monomer and/or aromatic epoxy (meth)acrylate is preferablypresent in the polymerizable composition in an amount of at least about15 wt-% (e.g. 20 wt-%, 30 wt-%, 35 wt-%, 40 wt-%, 45 wt-% and 50 wt-%and any amount there between). Typically, the amount of the firstmonomer and/or aromatic epoxy (meth)acrylate does not exceed about 60wt-%.

In addition to the first monomer and/or aromatic epoxy (meth)acrylate,the polymerizable composition of the invention can optionally include atleast one and preferably only one crosslinking agent. Multi-functionalmonomers can be used as crosslinking agents to increase the glasstransition temperature of the polymer that results from the polymerizingof the polymerizable composition. The glass transition temperature canbe measured by methods known in the art, such as Differential ScanningCalorimetry (DSC), modulated DSC, or Dynamic Mechanical Analysis.Preferably, the polymeric composition is sufficiently crosslinked toprovide a glass transition temperature that is greater than 45° C.

The crosslinking agent comprises at least two and preferably at leastthree (meth)acrylate functional groups. Suitable crosslinking agentsinclude for example hexanediol acrylate (HDDA), pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,trimethylolpropane tri(methacrylate), dipentaerythritolpenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate,trimethylolpropane ethoxylate tri(meth)acrylate, glyceryltri(meth)acrylate, pentaerythritol propoxylate tri(meth)acrylate, andditrimethylolpropane tetra(meth)acrylate. Any one or combination ofcrosslinking agents may be employed.

The crosslinking agent may be present in the polymerizable compositionin an amount of at least about 2 wt-%. Typically, the amount ofcrosslinking agent is not greater than about 25 wt-%. The crosslinkingagent may be present in any amount ranging from about 5 wt-% and about15 wt-%.

Preferred crosslinking agents include hexanediol diacrylate (HDDA),pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol penta(meth)acrylate, trimethylolpropanetri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, andmixtures thereof. Pentaerythritol triacrylate (PETA) anddipentaerythritol pentaacrylate are commercially available from SartomerCompany, Exton, Pa. under the trade designations “SR444” and “SR399LV”respectively; from Osaka Organic Chemical Industry, Ltd. Osaka, Japanunder the trade designation “Viscoat #300”; from Toagosei Co. Ltd.,Tokyo, Japan under the trade designation “Aronix M-305”; and fromEternal Chemical Co., Ltd., Kaohsiung, Taiwan under the tradedesignation “Etermer 235”. Trimethylol propane triacrylate (TMPTA) andditrimethylol propane tetraacrylate (di-TMPTA) are commerciallyavailable from Sartomer Company under the trade designations “SR351” and“SR355”. TMPTA is also available from Toagosei Co. Ltd. under the tradedesignation “Aronix M-309”. Further, ethoxylated trimethylolpropanetriacrylate and ethoxylated pentaerythritol triacrylate are commerciallyavailable from Sartomer under the trade designations “SR454” and “SR494”respectively.

In each embodiment described herein, the polymerizable resin compositionoptionally, yet preferably comprises up to about 35 wt-% (e.g. integersranging from 1 to 35) reactive diluents to reduce the viscosity of thepolymerizable resin composition and to improve the processability.Reactive diluents are mono-ethylenically unsaturated monomers such as(meth)acrylates or monomeric N-substituted or N,N-disubstituted(meth)acrylamides, especially an acrylamide. These includeN-alkylacrylamides and N,N-dialkylacrylamides, especially thosecontaining C₁₋₄ alkyl groups. Examples are N-isopropylacrylamide,N-t-butylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide,N-vinyl pyrrolidone and N-vinyl caprolactam.

Preferred diluents can have a refractive index greater than 1.50 (e.g.greater than 1.55. Such reactive diluents can be halogenated ornon-halogenated (e.g. non-brominated). Suitable monomers typically havea number average molecular weight no greater than 450 g/mole include

Suitable reactive diluents include for example phenoxy ethyl(meth)acrylate; phenoxy-2-methylethyl (meth)acrylate; phenoxyethoxyethyl(meth)acrylate, 3-hydroxy-2-hydroxypropyl (meth)acrylate; benzyl(meth)acrylate, 4-(1-methyl-1-phenethyl)phenoxyethyl (meth)acrylate;phenylthio ethyl acrylate; 2-naphthylthio ethyl acrylate; 1-naphthylthioethyl acrylate; 2,4,6-tribromophenoxy ethyl acrylate; 2,4-dibromophenoxyethyl acrylate; 2-bromophenoxy ethyl acrylate; 1-naphthyloxy ethylacrylate; 2-naphthyloxy ethyl acrylate; phenoxy 2-methylethyl acrylate;phenoxyethoxyethyl acrylate; 3-phenoxy-2-hydroxy propyl acrylate;2-phenylphenoxy ethyl acrylate; 4-phenylphenoxy ethyl acrylate;2,4-dibromo-6-sec-butylphenyl acrylate; 2,4-dibromo-6-isopropylphenylacrylate; benzyl acrylate; phenyl acrylate; 2,4,6-tribromophenylacrylate. Other high refractive index monomers such as pentabromobenzylacrylate and pentabromophenyl acrylate can also be employed.

The inclusion of only one diluent is preferred for ease inmanufacturing. A preferred diluent is phenoxyethyl (meth)acrylate, andin particular phenoxyethyl acrylate (PEA). Phenoxyethyl acrylate iscommercially available from more than one source including from Sartomerunder the trade designation “SR339”; from Eternal Chemical Co. Ltd.under the trade designation “Etermer 210”; and from Toagosei Co. Ltdunder the trade designation “TO-1166”. Benzyl acrylate is commerciallyavailable from AlfaAeser Corp, Ward Hill, Mass.

The optional high index monomer may be halogenated (i.e. brominated).One exemplary high index optional monomer is 2,4,6-tribromophenoxyethyl(meth)acrylate commercially available from Daiichi Kogyo Seiyaku Co. Ltd(Kyoto, Japan) under the trade designation “BR-31”.

Such optional monomer(s) may be present in the polymerizable compositionin amount of at least about 5 wt-%. The optional monomer(s) typicallytotal no more than about 50 wt-% of the polymerizable composition. Insome embodiments the total amount of optional high index monomer rangesfrom about 30 wt-% to about 45 wt-% (including integers between 30 and45).

The UV curable polymerizable compositions comprise at least onephotoinitiator. A single photoinitiator or blends thereof may beemployed in the brightness enhancement film of the invention. In generalthe photoinitiator(s) are at least partially soluble (e.g. at theprocessing temperature of the resin) and substantially colorless afterbeing polymerized. The photoinitiator may be (e.g. yellow) colored,provided that the photoinitiator is rendered substantially colorlessafter exposure to the UV light source.

Suitable photoinitiators include monoacylphosphine oxide andbisacylphosphine oxide. Commercially available mono or bisacylphosphineoxide photoinitiators include 2,4,6-trimethylbenzoydiphenylphosphineoxide, commercially available from BASF (Charlotte, N.C.) under thetrade designation “Lucirin TPO”; ethyl-2,4,6-trimethylbenzoylphenylphosphinate, also commercially available from BASF under the tradedesignation “Lucirin TPO-L”; andbis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide commercially availablefrom Ciba Specialty Chemicals under the trade designation “Irgacure819”. Other suitable photoinitiators include2-hydroxy-2-methyl-1-phenyl-propan-1-one, commercially available fromCiba Specialty Chemicals under the trade designation “Darocur 1173” aswell as other photoinitiators commercially available from Ciba SpecialtyChemicals under the trade designations “Darocur 4265”, “Irgacure 651”,“Irgacure 1800”, “Irgacure 369”, “Irgacure 1700”, and “Irgacure 907”.

The photoinitiator can be used at a concentration of about 0.1 to about10 weight percent. More preferably, the photoinitiator is used at aconcentration of about 0.5 to about 5 wt-%. Greater than 5 wt-% isgenerally disadvantageous in view of the tendency to cause yellowdiscoloration of the brightness enhancing film. Other photoinitiatorsand photoinitiator may also suitably be employed as may be determined byone of ordinary skill in the art.

Surfactants such as fluorosurfactants and silicone based surfactants canoptionally be included in the polymerizable composition to reducesurface tension, improve wetting, allow smoother coating and fewerdefects of the coating, etc.

The polymerizable compositions are energy curable in time scalespreferably less than five minutes such as for a brightness enhancingfilm having a 75 micron thickness. The polymerizable composition ispreferably sufficiently crosslinked to provide a glass transitiontemperature that is typically greater than 45° C. The glass transitiontemperature can be measured by methods known in the art, such asDifferential Scanning Calorimetry (DSC), modulated DSC, or DynamicMechanical Analysis. The polymerizable composition can be polymerized byconventional free radical polymerization methods.

The polymerizable compositions described herein may be advantageous forother optical materials such as microstructure-bearing optical articles(e.g. films). Exemplary optical materials include optical articles suchas lens films, LED encapsulants, free-standing lenses, unstructured(e.g. flat) films, multilayer films, retroreflective sheeting, opticallight fibers or tubes, and flexible molds (e.g. suitable for makingbarrier ribs for plasma display panels) and others.

DEFINITIONS OF TERMS USED WITHIN THE PRESENT DESCRIPTION

“Index of refraction,” or “refractive index,” refers to the absoluterefractive index of a material (e.g., a monomer) that is understood tobe the ratio of the speed of electromagnetic radiation in free space tothe speed of the radiation in that material. The refractive index can bemeasured using known methods and is generally measured using an Abberefractometer in the visible light region (available commercially, forexample, from Fisher Instruments of Pittsburgh, Pa.). It is generallyappreciated that the measured index of refraction can vary to someextent depending on the instrument.

“(Meth)acrylate” refers to both acrylate and methacrylate compounds.

“Polymerizable composition” refers to the total composition includingthe organic component that comprises at least one polymerizable monomerand the optional inorganic nanoparticles.

“Organic component” refers to all of the components of the compositionexcept for the inorganic nanoparticles and nanoparticle surfacemodifier(s). For embodiments wherein the polymerizable composition isfree of inorganic nanoparticles, the organic component and polymerizablecomposition are the same.

The term “nanoparticles” is defined herein to mean particles (primaryparticles or associated primary particles) with a diameter less thanabout 100 nm.

“Surface modified colloidal nanoparticle” refers to nanoparticles eachwith a modified surface such that the nanoparticles provide a stabledispersion.

“Aggregation” refers to a strong association between primary particlesthat may be chemically bound to one another. The breakdown of aggregatesinto smaller particles is difficult to achieve.

“Agglomeration refers to a weak association between primary particleswhich my be held together by charge or polarity and can be broken downinto smaller entities.

“Primary particle size” refers to the mean diameter of a single(non-aggregate, non-agglomerate) particle.

The recitation of numerical ranges by endpoint includes all numbersubsumed within that range (e.g. to the degree of precision for thenumerical endpoint). For example a relative gain of greater than 1.78and less than 2.05 includes 1.79, 1.80, 1.81, 1.82, etc., up to 2.04.

Each of the patents referenced herein are incorporated by reference intheir entirety.

Advantages of the invention are further illustrated by the followingexamples, but the particular materials and amounts thereof recited inthe examples, as well as other conditions and details, should not beconstrued to unduly limit the invention. All percentages and ratiosherein are by weight unless otherwise specified.

EXAMPLES

Refractive Index of the Polymerizable Compositions was Determined with aFischer Scientific Refractometer Co. Model # 6208.

Gain Test Method

Optical performance of the films was measured using a SpectraScan™PR-650 SpectraColorimeter with an MS-75 lens, available from PhotoResearch, Inc, Chatsworth, Calif. The films were placed on top of adiffusely transmissive hollow light box. The diffuse transmission andreflection of the light box can be described as Lambertian. The lightbox was a six-sided hollow cube measuring approximately 12.5 cm×12.5cm×11.5 cm (L×W×H) made from diffuse PTFE plates of ˜6 mm thickness. Oneface of the box is chosen as the sample surface. The hollow light boxhad a diffuse reflectance of ˜0.83 measured at the sample surface (e.g.˜83%, averaged over the 400-700 nm wavelength range, measurement methoddescribed below). During the gain test, the box is illuminated fromwithin through a ˜1 cm circular hole in the bottom of the box (oppositethe sample surface, with the light directed towards the sample surfacefrom the inside). This illumination is provided using a stabilizedbroadband incandescent light source attached to a fiber-optic bundleused to direct the light (Fostec DCR-II with ˜1 cm diameter fiber bundleextension from Schott-Fostec LLC, Marlborough Mass. and Auburn, N.Y.). Astandard linear absorbing polarizer (such as Melles Griot 03 FPG 007) isplaced between the sample box and the camera. The camera is focused onthe sample surface of the light box at a distance of ˜34 cm and theabsorbing polarizer is placed ˜2.5 cm from the camera lens. Theluminance of the illuminated light box, measured with the polarizer inplace and no sample films, was >150 cd/m². The sample luminance ismeasured with the PR-650 at normal incidence to the plane of the boxsample surface when the sample films are placed parallel to the boxsample surface, the sample films being in general contact with the box.The relative gain is calculated by comparing this sample luminance tothe luminance measured in the same manner from the light box alone. Theentire measurement was carried out in a black enclosure to eliminatestray light sources. When the relative gain of film assembliescontaining reflective polarizers was tested, the pass axis of thereflective polarizer was aligned with the pass axis of the absorbingpolarizer of the test system. Relative gain values reported forprismatic films were generally obtained with the prism grooves of thefilm nearest the absorbing polarizer being aligned perpendicular to thepass axis of the absorbing polarizer.

The diffuse reflectance of the light box was measured using a 15.25 cm(6 inch) diameter Spectralon-coated integrating sphere, a stabilizedbroadband halogen light source, and a power supply for the light sourceall supplied by Labsphere (Sutton, N.H.). The integrating sphere hadthree opening ports, one port for the input light (of 2.5 cm diameter),one at 90 degrees along a second axis as the detector port (of 2.5 cmdiameter), and the third at 90 degrees along a third axis (i.e.orthogonal to the first two axes) as the sample port (of 5 cm diameter).A PR-650 Spectracolorimeter (same as above) was focused on the detectorport at a distance of ˜38 cm. The reflective efficiency of theintegrating sphere was calculated using a calibrated reflectancestandard from Labsphere having ˜99% diffuse reflectance (SRT-99-050).The standard was calibrated by Labsphere and traceable to a NISTstandard (SRS-99-020-REFL-51). The reflective efficiency of theintegrating sphere was calculated as follows:Sphere brightness ratio=1/(1−Rsphere*Rstandard)

The sphere brightness ratio in this case is the ratio of the luminancemeasured at the detector port with the reference sample covering thesample port divided by the luminance measured at the detector port withno sample covering the sample port. Knowing this brightness ratio andthe reflectance of the calibrated standard (Rstandard), the reflectiveefficiency of the integrating sphere, Rsphere, can be calculated. Thisvalue is then used again in a similar equation to measure a sample'sreflectance, in this case the PTFE light box:Sphere brightness ratio=1/(1−Rsphere*Rsample)

Here the sphere brightness ratio is measured as the ratio of theluminance at the detector with the sample at the sample port divided bythe luminance measured without the sample. Since Rsphere is known fromabove, Rsample can be calculated. These reflectances were calculated at4 nm wavelength intervals and reported as averages over the 400-700 nmwavelength range.

ZrO₂ Sols

ZrO₂ sols were prepared in accordance with the procedures described inPublished U.S. Patent Application No. US2006/0204745 that claimspriority to U.S. patent application Ser. No. 11/078,468 filed Mar. 11,2005. The resulting ZrO₂ sols were evaluated with Photo CorrelationSpectroscopy (PCS), X-Ray Diffraction and Thermal Gravimetric Analysisas described in Published U.S. Patent Application No. US2006/0204745 andU.S. patent application Ser. No. 11/078,468. The ZrO₂ sols used in theexamples had properties in the ranges that follow:

PCS Data Intensity Volume- (Intensity- Dispersion avg size avg sizeavg)/(Volume- Index (nm) (nm) avg) 1.0-2.4 23.0-37.0 8.0-18.8 1.84-2.97

Relative Intensities Apparent Crystallite Size (nm) Weighted Cubic/ (C,T) M M Avg M Avg XRD Tetragonal Monoclinic (1 1 1) (−1 1 1) (1 1 1) Size% C/T Size 100 6-12 7.0-8.5 3.0-6.0 4.0-11.0 4.5-8.3 89%-94% 7.0-8.4Polymerizable Resin Composition 1

The ZrO₂ sol (100.0 g), methoxypropanol (100.0 g), BCEA obtained fromCytec Surface Specialties, Smyrna, Ga. (2.50 g),2-[2-(2-methoxyethoxy)ethoxy]acetic acid (“MEEAA”) obtained fromSigma-Aldrich, Milwaukee, Wis. (5.23 g), a 50/50 wt % blend ofphenylthiolethyl acrylate (“PTEA” obtained from Bimax) and BR-31 (20.78g), and a 5% solution of “Prostab 5198” obtained from Ciba Giegy (0.1 g)were charged to a 500 mL round bottom flask. Water and alcohol wereremoved via rotary evaporation such that he uncured refractive index ofthe resultant formulation was 1.6855 and it contained 57.5% ZrO₂.

Polymerizable Resin Composition 2

10.03 g of Polymerizable Composition 1 and 0.04 g of Lucirin TPO-L wereadded to a 25 mL amber vial. The vial was heated and mixed on a rolleruntil the sample was homogeneous. The mixed sample gave an uncuredrefractive index of 1.6835.

Polymerizable Resin Composition 3

10.05 g of Polymerizable Resin Composition 1 and 2.39 g of a 50/50 wt. %mixture of PTEA/BR-31 were added to a 25 mL amber vial. Next, 0.07 g ofLucirin TPO-L was added to the same vial. The vial was then heated andmixed on a roller until the sample was homogeneous. The mixed samplegave an uncured refractive index of 1.6425.

Polymerizable Resin Composition 4

10.07 g of Polymerizable Resin Composition 1 and 6.32 g of a 50/50 wt. %mixture of PTEA/BR-31 were added to a 25 mL amber vial. Next, 0.11 g ofLucirin TPO-L was added to the same vial. The vial was then heated andmixed on a roller until the sample was homogeneous. The mixed samplegave an uncured refractive index of 1.617.

Polymerizable Resin Composition 5

The ZrO₂ sol (100.00 parts by weight), MEEAA (4.44 pbw), BCEA (2.13pbw), 1-methoxy-2-propanol (115 pbw), a 50/50 mix of SR-339/BR31 (29.78pbw) and a 5 weight percent solution of Prostab 5198 in water (0.12 g)were charged to a round bottom flask. The alcohol and water were removedvia vacuum distillation such that the resulting resin had approximately53.3 weight percent zirconia and had an uncured refractive index of1.6525. Lucirin TPO-L was added to the mixture to provide a compositionthat contained 0.47 parts per hundred by weight of Lucirin TPO-L.

Polymerizable Resin Composition 6

10.06 g of Polymerizable Resin Composition 5 and 2.72 g of a 50/50 wt. %mixture of phenoxyethyl acrylate available from Sartomer Co., under thetrade designation SR 339/BR-31 were added to a 25 mL amber vial. Next,0.02 g of Lucirin TPO-L was added to the same vial. The vial was thenheated and mixed on a roller until the sample was homogeneous. The mixedsample gave an uncured refractive index of 1.617.

Polymerizable Resin Composition 7

10.18 g of Polymerizable Resin Composition 5 and 6.8 g of a 50/50 wt. %mixture of SR 339/BR-31 were added to a 25 mL amber vial. Next, 0.02 gof Lucirin TPO-L was added to the same vial. The vial was then heatedand mixed on a roller until the sample was homogeneous. The mixed samplegave an uncured refractive index of 1.597.

Polymerizable Resin Composition 8 (Control)

Ex. 1 of Table 1 of U.S. Pat. No. 6,355,754. (RDX51027/EB220/BR31/PEA/FC430 at a weight ratio of 30/20/37.5/12.5/0.3 and 1 (pph)Darocure 1173). The resin had an uncured refractive index of 1.562.

Polymerizable Resin Composition 9

50.5 g of Polymerizable Resin Composition 5 and 3.15 g of a 50/50 wt. %mixture of SR 339/BR-31 were added to a 25 mL amber vial. The vial wasthen heated and mixed on a roller until the sample was homogeneous. Themixed sample gave an uncured refractive index of 1.640.

Polymerizable Resin Composition 10

50.25 g of Polymerizable Resin Composition 5 and 6.12 g of a 50/50 wt. %mixture of SR 339/BR-31 were added to a 25 mL amber vial. The vial wasthen heated and mixed on a roller until the sample was homogeneous. Themixed sample gave an uncured refractive index of 1.633.

Polymerizable Resin Composition 11

50.42 g of Polymerizable Resin Composition 5 and 9.27 g of a 50/50 wt. %mixture of SR 339/BR-31 were added to a 25 mL amber vial. The vial wasthen heated and mixed on a roller until the sample was homogeneous. Themixed sample gave an uncured refractive index of 1.623.

Each of the resin compositions were prepared into variousmicrostructured optical films and optical film assemblies. Tables 1-9 asfollows report the relative gain values of the various films andassemblies.

Film Preparation A—Substantially Non-polarizing PrismaticMicrostructured Optical Film

An 8″×11″ metal master consisting of linear rows of 90 degree prismswith a nominal pitch spacing of 50 microns, similar to the prismgeometry pattern found on Vikuiti BEF II (commercially available from 3MCo., St. Paul, Minn.), was placed on a hot plate and heated to 140° F. A4 ml bead of the polymerizable resin (as set forth in the Tables) wasapplied to the master tool using a disposable pipette. Next, a 500 gaugePET available from Dupont Teijn Films as MELINEX 623 was placed on thebead of resin and master tool. The PET film was oriented so the linearprisms are oriented approximately perpendicular (90°±/−20°) to the highgain axis of the film. The master tool, resin and PET were then passedthrough a heated nip roll at 160° F. with sufficient force for the resinto fill the master tool completely, while eliminating any entrained air.The filled master tool was then exposed to ultraviolet radiation from a“D-bulb” using a P150 power supply available from Fusion UV Systems,Inc. Gaithersburg, Md. at a linespeed of 50 fpm for two passes. The PETfilm was then manually removed from the master tool. The prismaticcoating formed on the PET film resulted in a coating thickness ofapproximately 25 microns.

Film Preparation B—Reflective Polarizing Prismatic MicrostructuredOptical Film

The optical film was prepared in the same manner described in FilmPreparation A except the PET film was replaced with a reflectivepolarizer film as described in Example 3 of U.S. Patent Application Ser.No. 60/668873 filed Apr. 6, 2005) utilizing the Sahara SA 115 protectiveboundary layers; incorporated by reference.

Film Preparation C

The optical film was prepared in the same manner described in FilmPreparation B except that the master tool had a prism pattern thatconsisted of linear rows of 90 degree prisms with a nominal pitchspacing of 50 microns, where the linear prisms have a designedpseudo-random undulation in their peak height, similar to the prismgeometry pattern found on Vikuiti BEF III (commercially available from3M Co., St. Paul, Minn.).

TABLE 1 Single Sheet Relative Gain of Microstructured Non-PolarizingOptical Film (Film Preparation A) Microstructured Polymerizable SingleSheet Optical Film Example Resin Composition Relative Gain Ex. 1 Ex. 21.969 Ex. 2 Ex. 3 1.932 Ex. 3 Ex. 4 1.873 Ex. 4 Ex. 6 1.876 Ex. 5 Ex. 71.831 Ex. 6 Ex. 5 1.925 Ex. 7 - Control Ex. 8 1.748

For Table 2 as follows, an assembly was prepared wherein each of theprismatic microstructured optical films of Table 1 were stacked with anunstructured reflective polarizing film such that the pass axis of thereflective polarizing film was orthogonal to the prisms. The reflectivepolarizing film employed was the same as the base layer substratedescribed in Film Preparation B.

TABLE 2 Relative Gain of Assembly of Microstructured Non-PolarizingOptical Film and an Unstructured Reflective Polarizing FilmMicrostructured Polymerizable Assembly Optical Film Example ResinComposition Relative Gain Ex. 8 Ex. 2 2.751 Ex. 9 Ex. 3 2.724 Ex. 10 Ex.4 2.654 Ex. 11 Ex. 6 2.663 Ex. 12 Ex. 7 2.616 Ex. 13 Ex. 5 2.707 Ex.14 - Control Ex. 8 2.544

For Table 3 as follows, an assembly was prepared wherein each of theprismatic microstructured optical films of Table 1 were stacked with asecond piece of the same film. The prismatic microstructured surface ofthe bottom film was contacted with the base layer substrate of the topfilm such that the prisms of the bottom film were orthogonal with theprisms of the top film.

TABLE 3 Relative Gain of Assembly Comprising a Pair of the SameMicrostructured Non-Polarizing Optical Film Assembly PolymerizableSingle Assembly Example Resin Composition Sheet Example Relative GainEx. 15 Ex. 2 Ex. 1 3.191 Ex. 16 Ex. 3 Ex. 2 3.138 Ex. 17 Ex. 4 Ex. 32.947 Ex. 18 Ex. 6 Ex. 4 3.035 Ex. 19 Ex. 7 Ex. 5 2.937 Ex. 20 Ex. 5 Ex.6 3.120 Ex. 21 - Control Ex. 8 Ex. 7 2.762

For Table 4 as follows, an unstructured reflective polarizing film wasstacked above the assembly of Table 3 such that the pass axis of thereflective polarizing film was orthogonal to the prisms of the topsheet. The reflective polarizing film employed was the same as the baselayer substrate described in Film Preparation B.

TABLE 4 Relative Gain of Assembly Comprising a Pair of the SameMicrostructured Non-Polarizing Optical Films and a UnstructuredReflective Polarizing Optical Film Assembly Polymerizable SingleAssembly Example Resin Composition Sheet Example Relative Gain Ex. 22Ex. 2 Ex. 1 3.576 Ex. 23 Ex. 3 Ex. 2 3.618 Ex. 24 Ex. 4 Ex. 3 3.475 Ex.25 Ex. 6 Ex. 4 3.549 Ex. 26 Ex. 7 Ex. 5 3.481 Ex. 27 Ex. 5 Ex. 6 3.580Ex. 28 - Control Ex. 8 Ex. 7 3.330

TABLE 5 Single Sheet Relative Gain of Microstructured ReflectivePolarizing Optical Film (Ex. 29 and Ex. 30 Film Preparation B)Microstructured Polymerizable Single Sheet Optical Film Example ResinComposition Relative Gain Ex. 29 Ex. 5 2.492 Ex. 30 Ex. 2 2.904 Ex. 31 -BEF-RP 90/24 2.415 (commercially available from 3M Company)

For Table 6 as follows, an assembly was prepared wherein each of theprismatic microstructured optical films of Table 1 were stacked with aprismatic microstructured film of Table 5. The prismatic microstructuredsurface of the bottom film was contacted with the base layer substrateof the top film such that the prisms of the bottom film were orthogonalwith the prisms of the top film.

TABLE 6 Relative Gain of Assembly Comprising a MicrostructuredNon-Polarizing Optical Film and a Microstructured Reflective PolarizingOptical Film Assembly Bottom Film Top Film Relative Example ExampleExample Gain Ex. 32 Ex. 1 Ex. 29 3.350 Ex. 33 Ex. 2 Ex. 29 3.373 Ex. 34Ex. 3 Ex. 29 3.322 Ex. 35 Ex. 4 Ex. 29 3.373 Ex. 36 Ex. 5 Ex. 29 3.359Ex. 37 Ex. 6 Ex. 29 3.369 Ex. 38 Ex. 7 Ex. 29 3.307 Ex. 39 Ex. 1 Ex. 304.023 Ex. 40 Ex. 2 Ex. 30 4.027 Ex. 41 Ex. 3 Ex. 30 3.945 Ex. 42 Ex. 4Ex. 30 4.006 Ex. 43 Ex. 5 Ex. 30 3.990 Ex. 44 Ex. 6 Ex. 30 4.039 Ex. 45Ex. 7 Ex. 30 3.900 Ex. 46 Ex. 6 Ex. 31 3.399 Ex. 47 Ex. 7 Ex. 31 3.258Control

TABLE 7 Single Sheet Relative Gain of Microstructured Non-PolarizingOptical Film (Film Preparation C) Film Polymerizable Single SheetExample Resin Example Relative Gain Ex. 48 Ex. 5 1.918 Ex. 49 Ex. 91.892 Ex. 50 Ex. 10 1.875 Ex. 51 Ex. 11 1.860 Ex. 52 Ex. 8 1.741 Control

For Table 8 as follows, an assembly was prepared wherein each of theprismatic microstructured optical films of Table 7 were stacked with asecond piece of the same film. The prismatic microstructured surface ofthe bottom film was contacted with the base layer substrate of the topfilm such that the prisms of the bottom film were orthogonal with theprisms of the top film.

TABLE 8 Relative Gain of Assembly Comprising a Pair of the SameMicrostructured Non-Polarizing Optical Films Assembly PolymerizableAssembly Example Resin Example Relative Gain Ex. 53 Ex. 5 2.927 Ex. 54Ex. 9 2.906 Ex. 55 Ex. 10 2.867 Ex. 56 Ex. 11 2.833 Ex. 57 Control Ex. 82.636

For Table 9 as follows, an assembly was prepared wherein the prismaticmicrostructured surface of the indicated bottom film was contacted withthe base layer substrate of the indicated top film such that the prismsof the bottom film were orthogonal with the prisms of the top film.

TABLE 9 Relative Gain of Assembly Comprising a Pair of DifferentMicrostructured Non-Polarizing Optical Films Assembly Bottom Film TopFilm Relative Example Example Example Gain Ex. 58 Ex. 6 Ex. 48 3.006 Ex.59 Ex. 48 Ex. 6 2.977 Ex. 60 Ex. 4 Ex. 6 3.060

Table 9 illustrates that when a substantially non-polarizingmicrostructured optical film is combined with a second substantiallynon-polarizing microstructured optical film having a different (i.e.single sheet) relative gain, it is preferred to position themicrostructured optical film having the higher single sheet gain (e.g.lower absorption) at the top of a film stack assembly.

Polymerizable Resin Composition 12

The ZrO₂ sol was dialyzed for approximately 4.5 hr (Spetra/Por MembraneMWCO 12-14,000 available from VWR) to yield a stable sol at 36.395%ZrO₂. The dialyzed ZrO₂ sol (220.0 g), MEEAA (5.71 g), BCEA (4.10 g),1-methoxy-2-propanol (300 g), 2-(1-napthyloxy)-1-ethyl acrylate NOEA(29.98 g), TMPTA (12.85 g), BR31 (64.25 g) and a 5% solution of Prostab5198 in water (0.86 g) were charged to a round bottom flask and thealcohol and water were removed via rotary evaporation. The ZrO₂containing resin was 39.86% ZrO₂ and had a refractive index of 1.64. 0.6wt-% of TPO-L was added to the ZrO₂ containing resin and mixed together.

Polymerizable Resin Composition 13

Polymerizable Resin Composition 5 was diluted with a 50/50 mix ofBR-31/SR339 until the refractive index of the mixture was 1.64.

A Hewlett Packard 8453 Spectrophotometer was used with UV VIS ChemStation Rev. A. 02. 05 analysis software to measure the absorption ofPolymerizable Resins Compositions 12 and 13. The liquid polymerizableresin was tested in a quartz cuvette with a 1 cm path length. The resinwas tested at 100% solids, there was no dilution of the resin insolvent. A sample blank was run using the empty quartz cuvette. Theresults are shown in FIG. 3

Polymerizable Resins Compositions 12 and 13 were prepared intomicrostructured optical films in accordance with Film Preparation A.

Polymerizable Resin Composition Relative Gain Ex. 61 12 1.793 Ex. 62 131.829

An assembly was prepared wherein each of the prismatic microstructuredoptical films of Examples 61 and 62 were stacked with a second piece ofthe same film. The prismatic microstructured surface of the bottom filmwas contacted with the base layer substrate of the top film such thatthe prisms of the bottom film were orthogonal with the prisms of the topfilm.

Polymerizable Resin Composition Relative Gain Ex. 63 12 2.652 Ex. 64 132.807

Display Device Example 65

The assembly of Example 20 (i.e. a crossed sheet pair of substantiallynon-polarizing microstructured optical films prepared from apolymerizable resin having a refractive index of 1.6525) was compared toa crossed sheet pair of commercially available brightness enhancingfilms commercially available from 3M Company, St. Paul, Minn. under thetrade designation “Vikuiti BEF-II 90/50” in a LCD display.

The LCD module includes a CCFL light source, a wedge-shaped light-guidewith a dot extraction pattern, a multi-layer polymeric specularback-reflector behind the light-guide (sold by 3M Company, St. Paul,Minn. under the trade designation ESR [Enhanced Specular Reflector]), adiffusing film in front of the light guide, the assembly of crossedsheet brightness enhancement films in front of the diffusing film, adiffusing cover sheet in front of the BEF II sheets, and lastly atwisted nematic liquid crystal panel having absorbing polarizers on itsouter surfaces. Except for the ESR and brightness enhancing films, allthe display components were original to a 15.4″ LCD module, Hitachimodel 4074C, as provided in a commercially available Dell Latitude D800notebook computer system. The sheets of brightness enhancing opticalfilms are oriented such that prisms on each of the two sheets areorthogonal to each other, and are parallel/perpendicular to the CCFLlight source.

The light transmitted from the LCD module was characterized with anAutronic conoscope made by Autronic-Melchers GmbH, Karlsruhe, Germany.The Conoscopic Measurement Device provides a plot of luminance versusviewing angle in both the vertical and horizontal planes. FIG. 4includes a plot of luminance vs. vertical angle for the assembly ofExample 20 in comparison to an assembly of the commercially availablefilms. This plot demonstrates the improved light-refractive power of thefilms and assemblies of the invention. One effect of this greaterrefractive power is to direct the luminance peak on-axis. The peakluminance of the display including the assembly of Example 20 exhibits avertical angle substantially closer to zero. Brightness is maximized inthe display by placing the prism grooves of the microstructured filmnearest the rear absorbing polarizer of the LCD such that the prismgrooves are aligned substantially orthogonal to the pass axis of thatabsorbing polarizer. This advantage stems from geometric opticalprinciples and the preferred prism orientation applies to both standardprismatic films and the inventive films.

This display device was also tested using a diffuse white back-reflectorin place of the specular back-reflector together with the inventivefilms. In addition, the inventive films were tested both with andwithout a commercially available reflective polarizer in the device(Vikuiti DBEF-P2, available from 3M), these combinations also weretested with both types of back-reflectors. In all cases, measurablebrightness increases were found when using the inventive films comparedto standard films such as commercially available Vikuiti BEF-II.”

1. An optical film comprised of a light transmissible polymeric materialhaving a microstructured surface wherein the film is a reflectivepolarizing film having a single sheet relative gain of at least 2.46. 2.The optical film of claim 1 wherein the microstructured surfacecomprises a pattern of substantially parallel prisms coupled to areflective polarizing base layer having a pass axis wherein the prismsare orthogonal to the pass axis of the reflective polarizing film.
 3. Anassembly comprising the microstructured optical film of claim 1proximate a second optical film.
 4. The assembly of claim 2 wherein thesecond optical film is a turning film, a polarizing film, a diffuserfilm, or combination thereof.
 5. A device comprising: (a) a lightingdevice having a light-emitting surface; and (b) the optical film ofclaim 1 disposed proximate the light-emitting surface.
 6. The deviceaccording to claim 5, wherein the lighting device is a back-lit displaydevice.
 7. The device according to claim 5, wherein the lighting deviceis a back-lit liquid crystal display device.
 8. The device according toclaim 5, wherein the device is a handheld device, a computer display ora television.
 9. The device of claim 5 wherein the device comprises anabsorbing polarizer having a pass axis proximate a microstructuredoptical film comprising a pattern of substantially parallel prisms andthe prisms are substantially orthogonal to the pass axis of theabsorbing polarizer.